Method of mounting and construction of mounting for low frequency piezoelectric crystals



1955 F. H. FASTENAU, JR 2,699,508

METHOD OF MOUNTING AND CONSTRUCTION OF MOUNTING FOR LOW FREQUENCYPIEZOELECTRIC CRYSTALS Filed Dec.

INVENTOR 56 $40M, 5311/,

BY g i rade/420K A ORNEY United States Patent METHOD OF MOUNTING ANDCONSTRUCTION OF MOUNTING FOR LOW FREQUENCY PIEZO- ELECTRIC CRYSTALSFrederick H. Fastenau, Jr., Carlisle, Pa., assignor to Selectronics,Inc., Carlisle, Pa., a corporation of Delaware Application December 21,1951, Serial No. 262,848

6 Claims. (Cl. 3109.4)

My invention relates broadly to a piezo electric crystal system, andmore particularly to a method of fabrication and assembly and to animproved construction of holder for piezo electric crystals.

One of the objects of my invention is to provide a meth- 0d offabricating and assembling low frequency piezo electric crystals inholders or supports for utilization of maximum piezo electric activitytherefrom.

Another object of my invention is to provide :a holder for low frequencypiezo electric crystals operating below 2,000 kc.

Still another object of my invention is to provide a construction ofholder for low frequency piezo electric crystals in which the crystalsare notched along the Z axis and conductive materials introduced intothe notches to which mechanical and electrical connection may be madefor both mounting the crystals and establishing electric connection withelectrodes mounted on opposite faces thereof.

A further object of my invention is to provide a con struction ofmounting for low frequency piezo electric crystals for establishingconnection with the opposite electrodes of piezo electric crystals whichallow displace ment in three dimensions whereby vibration or shock towhich the piezo electric crystal may be subjected is prevented fromsetting up stresses or strains which may impair the mechanical orelectrical connection tothe piezo electric crystal.

A still further object of my invention is to provide a mounting meansfor piezo electric crystals in which a selection of materials has beenmade for filling notches formed in opposite peripheral edges of thepiezo electric crystals forming a conductive filler over which a coatingof electrically conductive material is applied for forming means forestablishing electrical connection with the filler and the electrodes ofthe piezo crystal adjacent thereto for insuring good mechanical andelectrical connection with thepiezo electric crystal with minimumobstruction to operation due to loading.

Other and further objects of my invention reside in the production of animproved resilient mounting for piezo electric crystals as set forthmore fully in the specification hereinafter following by reference tothe accompanying drawings, in which:

Figure l is an elevational view of a piezo electric crystal unitenclosed within a protective casing; Fig. 2 is a side elevational viewof the enclosed unit shown in Fig. 1; Fig. 3 is a vertical sectionalview taken through the piezo electric crystal unit of Figs. 1 and 2 andillustrating the manner of mounting the piezo electric crystal andestablishing electrical connection with the electrodes thereof; Fig. 4is a vertical sectional view taken on line 44 of Fig. 3; Fig. 5 is avertical sectional view taken on line 5-5 of Fig. 3; Fig. 6 is ahorizontal sectional view taken on line 6-6 of Fig. 3; Fig. 7 is ahorizontal sectional view taken on line 77 of Fig.3; Fig. 8 is anelevational view of the piezo electric crystal with the electrodesapplied thereto but prior to the mounting of the crystal on the springsupports; Fig. 9 is a fragmentary elevational view showing the manner ofnotching one edge of the piezo electric plate and the filling of thenotch with electrically conductive material; Fig. 10 is a view similarto the view shown in Fig. 9 but illustrating the addition of anelectrically conductive coating to the electrically conductive material,to which coating a mechanical and electrical connection is applied; Fig.11 is a side elevational view of one of the spring mounts for the piezoelectric crystal; and Fig. 12 is a front elevation-' al view of thespring mount illustrated in Fig. 11.

My invention is directed to a method of mounting piezo electriccrystals, particularly of low frequency characteristics, over afrequency range, for example, of 500 kc. to 2,000 kc., that is atfrequencies below 2,000 kc.

'The'conventional mounting for piezo electric crystals of has beenconsiderably reduced. The method of my invention involves the notchingof the piezo electric plate along the Z axis at opposite spacedpositions and the spotting in the notches of Hanover silver paste or DuPont liquid bright platinum 129. This material is electricallyconductive and serves as a partial filler for the notches of the piezoelectric plate. When liquid brightplatinum filler is used, anelectrically conductive silver coating is applied over the platinum toprovide a good soldering surface. I provide a pair of spring membersformed from resilient electric conductors having a diameter within therange of .O12-.0l8. These electrical conductors are tinned on theirsurfaces to rovide a good soldered connection with the plated silverwhich extends over the filler of silver paste or liquid bright platinum.Each of the resilient supports are formed into substantially rectangularloops which are resiliently supported by a vertically extending portionof the resilient members carried by a base of insulation material overwhich the protective casing for the device is fitted.

The small, compact size of the unit enables large num-; bers of theseholders to be assembled within small over-- all physical dimensions.

Referring to the drawings in more detail, reference character 1designatesa base frame which surrounds a base of insulation materialrepresented at 2 and provides a channel in which the dependingperipheral edge of housing 3 fits. The housing 3 is provided with aninterior lining 4 of insulation material. The base 2 provides a mountingmeans for a pair of spaced pins 5 and 6. The upper ends of the pinsprovide means for establishing a soldered connection 5a .and 6a with thelooped ends 7a and 8a of the resilient wire supports 7 and 8.

The upper ends of the resilient wire supports 7 and 8 are bent uponthemselves to form rectangular frames. These rectangular frames arebiased inwardly toward each other as shown more clearly in Fig. 3 andprovide mechanical mounting means and electric connection means with thepiezo electric plate designated at 10. Theparticular piezo electricplate illustrated is an 833 kc. crystal in the form of a circular disccontoured to a knife edge leaving a flat area of only ,1 diameter at thecenter. I use a 15 diopter lap to obtain this contour. The surfaces ofthe piezo electric plate are coated with an electrically conductivecovering forming the electrode on each face of the crystal. To securemaximum electrical conductivity I may use a gold coating or an alloy ofgold sputtered upon the opposite surfaces of the plate and forming anintimate surface connection with the surface of the piezo electricplate. One such electrode is represented at 11 and the other suchelectrode is shown at 12. Electrode 11 has a lug extension 11a projectedto one edge'of the plate. Electrode 12 has a lug extension 12a projectedto the opposite edge of the plate 10.

The crystal plate or disc 10 is provided with recesses or notches at theextreme limits of the Z axis as represented at 14 and 15 which have thecontour of a curve constituting segments of the disc. These recesses ornotches are filled with a layer of Hanover #150 silver paste or with DuPont liquid bright platinum 129 represented at 16. This layer ofmaterial after being introduced into the notches 14 and 15 is fired tosecure proper adhesion after which a layer of conducting material suchas silver 17 Patented Jan. 11, 1955 is applied to form the electrode.The piezo crystal may then be aligned with the inwardly biasedrectangular frames 71; and 8b of the resilient members 7 and 8 with thelower portions of the rectangular frames 7b and 8b registering with thesilver coatings l7 and 18 in the notches 14 and 15 respectively. Thelower portions of the rectangular frames 7 b and 8b are then soldered tothe silver coatings in recesses or notches 14 and 15. The solderedconnection between the lower portion of frame 7!) and the silver coating17 is completed to the lug 11a of electrode 11, thus establishing aconnection between pin and electrode 11 as represented, for example, at19 in Fig. 6. Correspondingly, the lower portion of frame 81) issoldered to the silver coating 13 and to the lug 12a of electrode 12 asrepresented at 20 in Fig.6. The upper portions of rectangular frames 7band 8b establish tangential contact with the peripheral edge of disc 10,thus clamping the disc in a position spaced above the base 2 asrepresented by gap 21 in Fig. 3. The low frequency piezo electriccrystal is thus free to move in the X, Y and Z axes without loading andwithout subjecting the bond between the crystal plate and the springmembers to excessive stresses or strains.

The fact that tinned music wire of a gauge extending between .012 and.018 is used in producing the resilient members 7 and 8 insures freedomof motion in all three planes without excessive loading of the crystal.The resiliency of the mounting is such that in extended vibration testsof this mounting the crystals rarely exceeded the frequency tolerance(.00075% Approximately 60% of the crystals vibrated change less than 10%in resistance and virtually all change less than While I haveillustrated a preferred form piezo electric crystal housing it is to beunderstood that other types of housings may be employed and that thehousing shown herein is to be considered in the illustrating sense andnot in the limiting sense.

I have found the method of mounting low frequency crystals as set forthherein and the structure of low frequency crystal mounting highlyefiicient and productive of uniform and reliable runs of low frequencycrystal. units so essential in communication equipment where space andweight limitations are essential, but I realize, however, thatmodifications in the details of the method and structure of my inventionmay be made and I desire that it be understood that no limitations uponmy invention are intended other than may be imposed by the scope of theappended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. A mounting for a low frequency piezo electric crystal of circulardisc-like contour, comprising a pair of resilient wire members supportedin spaced substantially parallel positions, said resilient wire memberseach being bent to form a substantially rectangular resilient peripheralframe having spaced substantially parallel extending end portionsaligned with each other on opposite sides of the peripheral edge of saidcrystal, one of the aligned end portions of each of the wire membersestablishing electrical connection with the piezo electric crystal alongthe Z axis thereof, another of the substantially parallel end portionsof each of said frames establishing tangential contact with theperipheral edge of said piezo electric crystal at positions remote fromthe Z axis of the piezo electric crystal and side portions forming partsof said frames and interconnecting the end portions thereof andextending in planes offset from the faces of said crystal.

2. A mounting for a low frequency piezo electric crystal comprising abase of insulation material, a pair of resilient wire members havingsupporting portions disposed in spaced positions on said base andextending in directions substantially normal to the plane of said base,said resilient wire members each having an open loop on the free endthereof extending in planes generally transverse to the axis of thesupporting portions of said wire members, a piezo electric crystalhaving its opposite edges projecting through the open loops on saidresilient wire members, whereby the crystal is displaceably clampedbetween said resilient wire members, one end of each of said loops beingelectrically and mechanically bonded to said piezo electric crystalalong the Z axis thereof and the remote end of each of said open loopsestablishing resilient engagement with opposite edges of the piezoelectric crystal in positions displaced from the Z axis of the piezoelectric crystal.

3. A mounting for a low frequency piezo electric crystal as set forth inclaim 2 in which the piezo electric crystal is substantially in the formof a circular disc and whereing the contact between opposite ends ofsaid loops and the peripheral edge of said piezo electric crystal at thepositions aligned at the Z axis of the crystal and displaced from the Zaxis thereof are'substantially tangential.

4. A mounting for a low frequency piezo electric crystal of the circulardisc type comprising a piezo electric crystal having an electrode oneach face thereof, with the electrode on one face of the piezo electriccrystal terminating in a connecting lug extending in the direction ofthe Z axis of the crystal and'the electrode on the opposite face of thecrystal terminating in a lug projecting in the opposite direction alongthe Z axis of the crystal, the periphery of said crystal being notchedin diametrically opposite positions along the Z axis of the crystal andin alignment with the aforesaid lugs, an electrically conductivematerial within each of said notches, an electrically conductive coatingextending over said material, electrically conductive resilient Wiremembers disposed adjacent opposite edges of said piezo electric crystaland supported at adjacent ends thereof, the free ends of said resilientwire members terminating in substantially rectangular frames havingopposite substantially parallel sides substantially embracing theopposite edges of said piezo electric crystal, one of each of thesubstantially parallel extending sides of said substantially rectangularframes being aligned with the Z axis of said crystal and electricallybonded to the electrically conductive material disposed in said notches,one of said resilient wires being bonded to the lug formed on one ofsaid electrodes and the other of said resilient wires being bonded tothe lug carried by the other of said electrodes and the upperextremities of said substantially rectangular frame members establishingtangential contact with said piezo electric crystal for suspending saidcrystal.

5. A mounting for a low frequency crystal comprising in combination witha substantially circular disc-like piezo electric crystal plate, a baseof insulation material, a pair of resilient wires projecting from saidbase and extending adjacent opposite peripheral edges of the crystalplate, said wires terminating in substantially rectangular peripheralframes each including a pair of spaced end portions extendingsubstantially normal to the plane of said crystal plate, one of said endportions of each frame being connected with opposite edges of said platealong the Z axis thereof in a position for locating the lower peripheraledge of said crystal plate in spaced relation to said base of insulationmaterial and the other of the end portions of each frame establishingyieldable tangential contact with the peripheral edge of said plate in aposition displaced from said Z axis.

6. A mounting for piezo electric crystals having a frequencycharacteristic below 2,000 kc., comprising in combination with a piezoelectric crystal plate having a frequency characteristic below 2,000kc., a pair of resilient wires each being formed in substantiallyrectangular peripheral frames for supporting said plate, said wires eachincluding a pair of spaced end portions interconnected by side portions,one of the said end portions of each of said frames establishingcontacting relation with the edge of said crystal along the Z axisthereof and the other of the said end portions of each of said framesestablishing contacting relation with the edge of said crystal inpositions displaced from the Z axis of the crystaland theinterconnecting side portions of said frames extending in planes spacedfrom the plane of said crystal plate.

References Cited in the file of this patent UNITED STATES PATENTS2,077,204 Bechmann Apr. 13, 1937 2,275,122 Ziegler Mar. 3, 19422,443,700 Sylvester June 22, 1948 2,484,428 Smith Oct. 1.1, 1949 FOREIGNPATENTS 985,072 France July 13, 1951

